Methods of determining the accuracy of density-calibrated images are well known in the art as means for preventing error in density measurements due to changes in properties over time or lot variations. One such method disclosed in Japanese unexamined patent application publication No. HEI-6-331630 involves performing density measurements on samples having known densities and correcting changes over time of image densities based on the results of these measurements.
In this conventional method, after first setting the samples used for calibrating image density, the densities of all samples are measured. If the measured density is determined to be within a preset range, then it is determined whether results of density measurements corresponding to all samples fall within a preset range. If the results of density measurements are found to fall within the preset range for all samples, the calibration results are determined to be normal and density calibration is performed based on these results. However, if the density measurement results for any sample are found to fall outside the preset range for that sample, then the calibration results are determined to be abnormal.
Accordingly, when repeating image density calibration, density measurements must be obtained not only for samples yielding abnormal results, but also for samples yielding normal results. Consequently, samples are unnecessarily consumed by repeating calibration for samples yielding normal results.